Driveline Vibration

[J.Kidd]

Started noticing a month ago...and surprisingly it has not gone away.

Symptoms:
Part 1:
First thing I noticed was when I took her out after washing to clear stubborn water off, I noticed a relatively soft "clunk" when shifting (casual shifting, not accelerating too hard). It didn't do it all the time, and if I was more ginger with my clutch engagement, it didn't do it. But, casual acceleration with casual gear changes would result in a noticeable (sound and feel) clunk.

Part 2:
The next thing I became aware of was an occasional vibration at speeds over 75. This vibration is not constant, but more cyclical when I feel it. I would feel a vibration for 4-5 seconds then it would disappear for 2-3 seconds, and then return....and this would just repeat.

Upon experimenting (ie. coasting with the clutch in, coasting with the clutch out), I have determined that the vibration is coming from the driveshaft. Coasting, engaging the clutch or not, does not eliminate the vibration.

I am suspecting either U-joints or carrier bearing. Aside from CAI and tune, the car is pretty much stock (2011 GT with 80k miles). Anyone have experience with this?

 

[Sky Render]

Transmission mount?

 

[J.Kidd]

Didn’t think of that! Basically gotta crawl under there and see what moves. But thanks, you gave me something else to look at when I’m under there.

 

[Dino Dino Bambino]

I am suspecting either U-joints or carrier bearing.

You're on the right track. Raise the car on a lift and check if there's excessive play in either of those areas.
The u-joint is easy to replace but the carrier bearing is non-servicable and would necessitate replacing the whole driveshaft. Good excuse to get an aluminum unit and save ~20lb too.

 

[MasterofDisaster]

Decades ago I had a terrible vibration coasting in my 1967 notchback, but couldn't find the source until the car was in park on jackstands. The rear wheels turned almost a half turn because the U joints were bad. Changed the U joints, vibration went away. You don't need a press if you have a C clamp that is big and burly enough to install the new U joints.

 

[J.Kidd]

Anyone have any idea how much the carrier bearing/bushing is supposed to move?

U-joints were SOLID. Transmission mount felt good as well. But, the carrier bearing had a good amount of movement to it. It almost seemed as though if I had the room, I could have pulled the rubber bushing up and out of the housing. Also seemed like the entire bushing was pushed forward...in the sense that there seemed to be a recess coming in from the back and none in front.

Just want to get some sort of confirmation that the play I experienced is excessive before I drop a few hundred on a new driveshaft.

Thanks for any help.